Swim fins, also called flippers or swimming fins, are used in water related activities to increase the surface area of the user's foot. With the larger surface area, the user is able to displace more water and propel themselves much faster relative to the water medium than with a bare foot.
Thus, fins are constructed with a substantial increase in surface area. The increase is made primarily in the blade portion, e.g., roughly the area forward of the user's toes and to a lesser extent the sides of the user's foot to gain maximum advantage from the portion of the leg muscles that are strongest during the propulsion component of a swim kick, the up beat.
Increasing the surface area provides significant benefits for some users. However, a large blade provides distinct disadvantages for other users, especially users who want or need a fast cycle of kicking since on the non-propulsion component of a swim kick, e.g., the down beat, the enlarged blade portion creates drag that must be overcome.
For example, a dive fin has relatively large surface area in comparison to other fin types to overcome the additional weight that scuba divers carry. Accordingly, divers typically swim at languid pace. The same fin is unsuitable for race swimmers, who swim at a fast rate. The drag induced by the large blade portion would hinder the swimmer on the down beat.
Such race swimmers condition their arms and shoulders in addition to their legs. When training, swimmers seek to achieve a high cycle rate of shoulder and arm movement alongside a leg movement. However, when training for a prolonged period of time, the legs often tire before the arms and shoulders, because the legs unlike the arms are constantly in water and must fight against water resistance. Thus, race swimmers turn to swim fins to maintain a training pace.
Swim fins having large blade portions are not suitable to establish and maintain a training pace. Thus, various solutions have been suggested to provide a fin that is suitable for training. Typically, these solutions involve shortening the blade portion so that the user has less drag than with a large blade and can increases the frequency of kicks, e.g., beats. See for example, U.S. Pat. No. 5,108,328.
By increasing the frequency, the swimmer is able to condition parts of their body that could not be conditioned as the swimmers legs tire from the frequent kicks. Thus, a short-swim fin provides an opportunity for a race swimmer to condition their arms and shoulders while permitting the legs to kick at a sustained rate.
However, simply shortening the blade fails to address that a swimmer has different needs during the kick. When the swim kick is in the up beat, e.g., propulsion portion of the kick, the swimmer's need is to propel themselves fast as possible. In contrast, when the kick is the down beat, e.g., retracting leg motion, the swimmer's need is to reduce drag so that the swimmer can kick again, e.g., increase the frequency of the kicks.
Another solution is to maintain the enlarged blade portion and make the fin more flexible. However, this leads to a fin having a large size that is difficult to maneuver on land and difficult to use in race swimming circumstances including turns made against a wall in a pool.
Thus, what is desired is a swim fin suitable for swim training and which permits a greater kick frequency and ease of use.